YoutubeDL.py

import urllib2, urlparse, sys, webbrowser

itags = {'45': 'webm_720p',
         '44': 'webm_480p',
         '43': 'webm_360p',
         '38': 'mp4_3072p',
         '37': 'mp4_1080p',
         '36': 'phone_mp4_240p',
         '35': 'flv_480p',
         '34': 'flv_360p',
         '22': 'mp4_720p',
         '18': 'mp4_360p',
         '17': 'phone_mp4_144p',
          '5': 'flv_240p'}

order_preference = ['18', '22', '34', '35']

def main():
    v_id = None
    if (len(sys.argv) > 0):
        try:
            v_id = urlparse.parse_qs(sys.argv[1].split('?')[1])['v'][0]
        except Exception:
            v_id = None
    if not v_id:
        print repr(sys.argv)
        return
    config = urllib2.urlopen('http://www.youtube.com/get_video_info?&video_id=%s&el=detailpage&ps=default&eurl=&gl=US&hl=en' % v_id).read()
    config = urlparse.parse_qs(config)
    formats = [urlparse.parse_qs(x) for x in config['url_encoded_fmt_stream_map'][0].split(',')]
    filtered_formats = dict([(x.get('itag', [0])[0], x) for x in formats if x.get('itag', [0])[0] in order_preference])
    sorted_formats   = [filtered_formats[x] for x in order_preference if filtered_formats.has_key(x)]
    first_pick = sorted_formats[0]
    download_url = first_pick['url'][0]
    if first_pick.has_key('sig'):
        download_url += ('&signature=' + first_pick['sig'][0])
    download_url = download_url.replace('http://', 'iDownloads://')
    webbrowser.open(download_url)

if __name__ == '__main__':
    main()

# Bookmarklet:
# javascript:window.location='pythonista://YoutubeDL?action=run&argv='+encodeURIComponent(document.location.href);

javascript:window.location='pythonista://YoutubeDL?action=run&argv='+encodeURIComponent(document.location.href);

最后找到一个可用的project . https://github.com/rg3/youtube-dl 挺好用
python main.py www.youtube.com/watch?v=wYowgVn5_8w